I'm partial to Black Ops, as I think the 60's: Russia and Vietnam setting was interesting. Far more original than yet another WWII game.
But as everyone else said, you can get the WaW Zombie Maps for Black Ops.
Ascension FTW!

But the WaW maps are different in Black Ops.
Anyway, WaW seems like the last Call of Duty game that cared about what the gamers wanted and less about how much money they could svck from the saps who buy the same tired recipe every year. Battlefield 3 is still better though, and if they added in a Zombie mode (which of course will never happen), it'd be the best thing since pants.
Although sometimes I rather play the fast-paced action of Call of Duty versus the realistic action of Battlefield 3. That's why you gotta have both!